1. Field of the Invention
This invention relates to handheld heat-generating tools, such as soldering tools. The invention is especially directed to gas-powered, catalyst-heated portable soldering tools, in particular, soldering irons.
2. Description of the Related Art
A diversity of constructions of portable soldering tools are known, including U.S. Pat. No. 4,133,301, which discloses a gas-powered soldering tool having various different constructions of soldering tip. An older construction of gas-powered soldering iron is described in U.S. Pat. No. 2,807,317, in which heating is effected by gas combustion rather than by a combustion catalyst. A further flame combustion type soldering tool is disclosed in U.S. Pat. No. 4,119,088. Yet another flame-heated soldering tool is described in DE 9602, while DE 1,253,020 is also directed to a combustion-based soldering tool.
EP-A-0,118,282 and corresponding U.S. Pat. No. 4,785,793 are directed to a soldering tool having a soldering tip with a tip portion and a housing to the rear of the tip portion. A catalytic element is located in a combustion chamber of the tool and arrangements are provided for supplying fuel to the catalytic element to heat the soldering tip. A particular feature of the arrangement is that the tip is carried solely by an internal support which extends from the tip through the combustion chamber to the fuel supply portion of the structure. This internal support serves to distribute fuel to the catalytic element and to conduct heat from the combustion chamber into the soldering tip portion.
A particular feature of catalytically-heated devices is the necessity for an initial flame-heating or thermal combustion phase and the concomitant need to terminate this phase when the catalyst is sufficiently hot to sustain continuing catalytic heating. A diversity of techniques are known for addressing this problem.
In U.S. Pat. No. 4,502,465, there is described a catalyst combustion curling device in which initial heating of the catalytic element is effected by flame heating. Initial forward movement of an operator member closes off an air hole, following which ignition takes place. Flame combustion is supported while the air hole remains closed, and is terminated by a reverse movement of the operator member, which results in the air hole being opened again, this causing a greater intake of air and extinguishing the flame. Catalytic heating then continues.
In U.S. Pat. No. 4,920,952 and corresponding GB 2,208,540A, a similar type of apparatus is described in which a gas/air mixture is piezoelectrically ignited to heat a combustion catalyst by an ignited flame. Subsequent flameless catalytic heating continues following flame extinction, which is effected by an arrangement enabling the gas/air ratio within the unit to be varied. In this way, a ratio suitable for ignition may be initially effected, then transformed into a ratio which brings about flame extinction, and finally the gas/air ratio may be adjusted for continuing catalytic combustion.
GB 2,156,964A describes a soldering iron using liquefied gas as a heat source, in which the gas from the liquefied gas tank is mixed with air and then directed to a combustion chamber for complete and flameless catalytic combustion. A shutter mechanism opens ignition ports at the inlet of the combustion chamber upon ignition of the mixture, for initial flame heating of the catalyst. These ports are closed after ignition of the gas mixture.
U.S. Pat. No. 4,552,124 is another example of a flameless combustion heating unit in which catalytic action is initially engendered by flame heating, and a shutter mechanism closes ports after completion of the ignition phase.
Disadvantages of arrangements such as those noted above in which one or more slideable members close off one or more ports or air holes is that for flame ignition to take place, a correct air to gas mixture ratio must be achieved. The achievement of such a correct ratio requires regulation of gas flow and Venturi or orifice size. Flame extinction involves displacement of a slideable member to usually close the ports or air holes, thereby upsetting the air/gas mixture required to support flame combustion and resulting in flame extinction. Such arrangements may be accompanied by an inefficient mixture of air and gas, this being consumed by the catalyst.
U.S. Pat. No. 5,215,456 is directed to an alternative manner of flame extinction from those previously described, in this instance by providing an actuating mechanism in the form of a bimetallic strip to bring a diffusion member into and away from the entrance of the combustion chamber. As described in this document, the diffusion member is initially placed in the flow of gas to establish flame combustion, and according as the bimetallic strip bearing the diffusion member heats up, the diffuser is then displaced out of the gas flow and flame combustion is terminated. Disadvantages of this arrangement are the relatively slow speed of operation of the bimetallic strip and the likelihood of its rusting or otherwise corroding with the passage of time. According as corrosion develops, which is likely because of the adverse conditions under which it operates, the bimetallic strip will cease to function. A further disadvantage is that when the unit is switched off, the bimetallic strip will take some time to cool and therefore a certain amount of time will pass before the diffuser is restored to the initial flame combustion position. While the strip is moving back to this initial or rest position, the unit will be unusable and must be set aside until such time as it is cooled down.
A non-catalytic unit is described in U.S. Pat. No. 4,815,441, in which two nozzles are provided for quick initial heating. A bimetallic strip terminates the heating action of one of the two nozzles, when the level of heat is sufficient, with the flame from the second nozzle continuing to heat the active portion of the unit. The flame is accommodated within a gauze enclosure, in the manner of a Davy lamp, thereby preventing ignition of combustible material to the exterior of the gauze.
A further necessity in catalytically heated devices is the need to maintain the evaporative process in the gas release valve, where the liquid gas is vaporised. In U.S. Pat. No. 5,215,076, as in EP-A-0,118,282 and corresponding U.S. Pat. No. 4,785,793, already discussed above, the possibility again exists of heat transfer through a heat transfer member from the combustion chamber of the unit to the gas discharge nozzle. Such an arrangement serves to maintain evaporation once combustion and catalytic action have been established, but does not assist in establishing initial evaporation when attempting to start up a unit from a cold condition.
In U.S. Pat. No. 4,785,793, a finned retaining collet is provided, but this serves to dissipate heat away from the plastic housing of the structure, rather than conduct heat to the nozzle area for gas evaporation.